1. Field of the Invention
This invention generally relates to a rotary power transmitting coupling device, and, in particular, to a speed responsive centrifugal clutch suitable for use as a lock-up clutch in a torque converter.
2. Description of the Prior Art
In a torque converter, there is commonly used a lock-up clutch which establishes a mechanical coupling by bringing an input shaft on the driving side into frictional contact with an output shaft on the driven side as the rotational speed increases thereby increasing the centrifugal force. Such a lock-up clutch is well known in the art and it commonly includes a shoe assembly which is brought into frictional contact with the driving surface which moves radially outward as the rotational speed and hence the centrifugal force increases. A typical shoe assembly is disclosed in U.S. Pat. No. 4,305,493 issued to Silberschlag on Dec. 15, 1981 and U.S. Pat. No. 4,226,309 issued to Silberschlag on Oct. 7, 1980.
As described in U.S. Pat. No. 4,117,918 issued to Silberschlag on Oct. 3, 1978, it is also known to provide a damper in such a lock-up clutch so as to obtain a smooth transmission of power from the driving side to the driven side through the shoe assembly. It is true that the power transmission can be carried out smoothly with the provision of such a damper, but this would tend to make the entire structure larger in size and heavier in weight. Since the lock-up clutch itself is already relatively large in size, a further addition of size would bring about various disadvantages, such as difficulty in handling and installation, heavy weight and high manufacturing cost.